1. Field of the Invention
The present invention relates to a vehicle which can turn with a smaller turning radius.
2. Description of the Related Background Art
For four-wheel vehicles, a parameter called the xe2x80x9cturning radiusxe2x80x9d is known for indicating the performance of each four-wheel vehicle. A vehicle having a smaller turning radius can make a smaller turn at a corner during a turning operation such as U-turn.
Vehicles employing four-wheel steering (4WS) have been known as prior art four-wheel vehicles which can improve the turning radius. The 4WS refers to a system which controls the steering angle (rudder angle) of not only front wheels but also rear wheels in association with a manipulation through a steering wheel. The 4WS system can reduce the turning radius due to the controllable steering angle provided to the rear wheels.
A fifth wheel system is also known as an improvement in the turning radius. The fifth wheel system additionally has a fifth wheel stored below the floor, in addition to four wheels, such that the fifth wheel is slightly protruded relative to the other wheels during a turn to lift up the vehicle body, and the fifth wheel is driven to have the vehicle make a turn.
However, the 4WS, while it is effective in reducing the turning radius, suffers from limitations to the reduction in the turning radius since the steering angle is limited in order to suppress an inherent shake-out phenomenon to a practically ignorable extent. The fifth wheel system in turn is expected to provide significant effects, but implies a problem that the vehicle becomes unstable due to a three-wheel state during a turning operation.
Moreover, since a vehicle turning operation which reduces the turning radius requires actuation of a turning mechanism which cannot be used during a normal running operation such as straight traveling and backward traveling, the vehicle presents another problem that it has only limited operation states in which the vehicle can be turned with stability.
Conventional vehicles also have a problem that drivers encounter difficulties in performing a turning operation with a good operability.
It is therefore an object of the present invention to provide a four-wheel vehicle which is capable of stably turning the vehicle body with a relatively small turning radius. It is another object of the present invention to provide a four-wheel vehicle which is capable of permitting a driver to perform a turning operation with a good operability.
A four-wheel vehicle equipped with a turning mechanism according to the present invention comprises a rotatably supporting device for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; an instructing device for generating a turn mode instruction in response to a manipulation; a determining device for determining whether a vehicle operating state satisfies predetermined conditions when the turn mode instruction is generated; a rotation driving device, when the determining device determines that the predetermined conditions are satisfied, for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; and turn driving device for applying a rotating torque to the one pair of left and right wheels at the angular positions along the tangential directions to turn the vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels.
According to the four-wheel vehicle of the present invention described above, since one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, are supported for rotation concerning the respective axes perpendicular to the ground, and the one pair of left and right wheels are rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions of the arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels, it is possible to provide a relatively simple and small turning mechanism. In addition, since the one pair of left and right wheels will not be rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions for a turning operation unless the vehicle operating state satisfies the predetermined conditions suitable for a turn when a turn mode instruction is generated, the turning operation can be performed while the vehicle is in a stable state. Further, since the one pair of left and right wheels are applied with a rotating torque at angular positions along tangential directions to turn the vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels, the turning radius is extremely small.
The four-wheel vehicle includes a left turn instructing device for generating a left turn instruction in response to a manipulation, and a right turn instructing device for generating a right turn instruction in response to a manipulation, wherein the turn driving device turns the vehicle body counterclockwise in response to the left turn instruction, and turns the vehicle body clockwise in response to the right turn instruction. According to this configuration, the vehicle body can be turned either in the clockwise or counterclockwise direction with a simple manipulation.
The left turn instructing device and the right turn instructing device are arranged integral with a steering wheel. According to this configuration, the driver can readily perform a left turn or a right turn operation while holding the steering wheel.
The four-wheel vehicle comprises a transmission formed with a left turn shift position and a right turn shift position in addition to shift positions for transmission, wherein the left turn instructing device generates the left turn instruction when a shift lever of the transmission is moved to the left turn shift position, and the right turn instructing device generates the right turn instruction when the shift lever of the transmission is moved to the right turn shift position. According to this configuration, the driver can readily perform a left turn or a right turn operation by manipulating the shift lever of the transmission.
The instructing device generates a turn mode stop instruction in response to a manipulation, and the rotation driving device rotates the one pair of left and right wheels from the angular position along the tangential directions to the straight traveling positions in response to the turn mode stop instruction. According to this configuration, after the vehicle body is turned, the one pair of left and right wheels can be rotated to the original straight traveling positions by a manipulation of the driver.
The predetermined conditions include at least the following conditions:
(a) the vehicle stops running; and
(b) the steering angle of front wheels is substantially zero degrees. By thus defining the predetermined conditions, it is possible to confirm whether vehicle is in a state from which the vehicle can transition without any problem to a vehicle body turning operation for which the one pair of left and right wheels are driven to rotate.
The condition defining that the vehicle stops running is detected from a shift position of a transmission equipped in the vehicle lying in a P (parking) position or an N (neutral) position, or a side brake being in operation. According to this detecting feature, it is possible to detect that the vehicle is not merely temporarily stopped, thereby preventing the vehicle from running forward or backward during a turning operation.
The turn driving device stops turning the vehicle body when the left turn instruction and the right turn instruction are being simultaneously generated. According to this configuration, it is possible to selectively instruct to turn the vehicle counterclockwise, to turn the vehicle clockwise, and to stop turning the vehicle only by manipulating the left turn instructing device and the right turn instructing device.
The rotation driving device includes a turn position detecting device for detecting that the one pair of left and right wheels have been rotated from the straight traveling positions to the angular positions along the tangential directions to generate a turn position signal, and the rotation driving device stops rotating the one pair of left and right wheels in response to the turn position signal. According to this configuration, since the driving of the one pair of left and right wheels for rotation are immediately stopped when the one pair of left and right wheels have been driven to rotate to the angular positions for turning the vehicle, the driver can proceed to a vehicle body turning operation.
The rotation driving device includes a straight traveling position detecting device for detecting that the one pair of left and right wheels have been rotated from the angular positions along the tangential directions to the straight traveling positions to generate a straight traveling position signal, and the rotation driving device stops rotating the one pair of left and right wheels in response to the straight traveling position signal. According to this configuration, since the driving of the one pair of left and right wheels for rotation are immediately stopped when the one pair of left and right wheels have been driven to rotate to the original straight traveling positions for stopping the vehicle body turning operation, the driver can return to a normal operation.
The vehicle further comprises a shift lock mechanism for disabling the transmission to perform a shifting operation when at least the one pair of left and right wheels are at positions other than the straight traveling positions. According to this configuration, since the vehicle is disabled to travel straight by the shift lock mechanism when the one pair of left and right wheels are at the angular positions rotated from the straight traveling positions for turning the vehicle body, it is possible to prevent erroneous manipulations by the driver.
The turn driving device applies the rotating torque to the one pair of left and right wheels with a driving source different from the driving source to turn the vehicle body. According to this configuration, unlike a normal driving source for running, a driving source capable of producing a minimally required driving force is sufficient, so that a smaller driving source can be driven for the turning operation in order to save the space.
The rotatably supporting device includes a trailing arm for rotatably supporting the one pair of left and right wheels through knuckles at the respective axes perpendicular to the ground of the one pair of left and right wheels. According to this configuration, since the rotatably supporting device is formed of existing suspension members, neither dedicated parts nor members are required for use in implementing the rotatably supporting device, thereby making it possible to reduce the cost.
The turn driving device includes a braking device for applying a braking force to rotations of the one pair of left and right wheels in response to a manipulation on a switch arranged in the steering wheel. According to this configuration, the driver can stop turning the vehicle body by manipulating the switch while holding the steering wheel.
The turn driving device includes a braking device for applying a braking force to rotations of the one pair of left and right wheels in response to stepping on a brake pedal. With this configuration, the driver can stop turning the vehicle body by stepping on the brake pedal in a manner similar to in a normal operation, thereby making it possible to readily stop turning the vehicle body at a desired position.
A four-wheel vehicle equipped with a turning mechanism according to the present invention comprises a rotatably supporting device for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; an instructing device for generating a turn mode instruction in response to a manipulation; a determining device for determining whether a vehicle operating state satisfies predetermined conditions when the turn mode instruction is generated; a rotation driving device, when the determining device determines that the predetermined conditions are satisfied, for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; and a turn driving device for applying rotating torques in rotating directions different from each other to the other pair of left and right wheels at angular positions along tangential directions to turn the vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels.
According to the four-wheel vehicle of the present invention described above, since one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, are supported for rotation concerning the respective axes perpendicular to the ground, and the one pair of left and right wheels are rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions of the arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels, it is possible to provide a relatively simple and small turning mechanism. In addition, since the one pair of left and right wheels will not be rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions for a turning operation unless the vehicle operating state satisfies the predetermined conditions suitable for a turn when a turn mode instruction is generated, the turning operation can be performed while the vehicle is in a stable state. Further, since the other pair of left and right wheels are applied with rotating torques at angular positions along tangential directions to turn the vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels, the turning radius is extremely small.
The turn driving device applies the rotating torques in rotating directions different from each other to the respective left and right wheels of the other pair with a driving source different from the driving source to turn the vehicle body. According to this configuration, like the aforementioned case, a driving source capable of producing a minimally required driving force is sufficient, unlike a normal driving source for running, so that a smaller driving source can be used to drive the wheels to rotate for the turning operation in order to save the space.
The turn driving device further includes a device for fixing a case for rotatably supporting two pinions arranged in a differential during a turning operation of the vehicle body, and a motor for driving one of side gears arranged in the differential for rotation. According to this configuration, since a differential function, i.e., rotation of the one driving axle with the case of the differential maintained fixed causes the other driving axle to reversely rotate, can be effectively utilized, a diving force for turning the vehicle body can be provided only by adding a minimally required function.
Further, a vehicle equipped with a turning mechanism according to the present invention comprises a rotatably supporting device for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; a rotation driving device for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; motors for applying rotating torques to the one pair of left and right wheels at the angular positions along the tangential directions to turn a vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels; a turn instructing device for generating a left or right turn instruction in response to a manipulation; and a voltage applying device for applying the motors with a gradually increasing driving voltage in response to the turn instruction.
In the four-wheel vehicle of the present invention described above, as a left or right turn instruction is generated in response to a manipulation, the motors are applied with a gradually increasing driving voltage, such that the motors apply rotating torques to the one pair of left and right wheels to turn the vehicle body on a neighborhood of a center point of the rotating axle for running the vehicle of the other pair of left and right wheels, so that the turning speed is gradually increased in the counterclockwise or clockwise turning direction. Therefore, the vehicle is prevented from suddenly turning immediately after the left or right turning instruction is generated, so that the driver can turn the vehicle body to a desired position with a good operability.
The voltage applying device gradually increases the driving voltage for a predetermined time, and thereafter maintains the driving voltage at a constant level. In this way, it is possible to prevent a turning speed from excessively increasing.
The motors rotate the one pair of left and right wheels in the counterclockwise direction in response to the left turn signal to turn the vehicle body counterclockwise, and rotate the one pair of left and right wheels in the clockwise direction in response to the right turn signal to turn the vehicle body clockwise. According to this configuration, the vehicle body can be turned either in the counterclockwise or clockwise direction with a simple manipulation.
The motors are provided for the respective left and right wheels of the one pair. With this configuration, each of the left and right wheels forming the pair can be driven for rotation with a simple structure.
The four-wheel vehicle further includes a turn stop instructing device for generating a turn stop instruction in response to a manipulation; and a braking force applying device for applying the motors with a gradually increasing braking force in response to the turn stop instruction. According to this configuration, since the turning speed is gradually decelerated in response to a manipulation performed by the driver when he wants to stop turning the vehicle body, the turning speed will not be suddenly decelerated, thereby allowing the driver to readily stop turning the vehicle body to place the vehicle at a desired position.
The turn instructing device and the turn stop instructing device are arranged integral with a steering wheel. According to this configuration, the driver can perform a turning operation while holding the steering wheel.
Also, a four-wheel vehicle equipped with a turning mechanism according to the present invention comprises a rotatably supporting device for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; a rotation driving device for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; motors for applying rotating torques to the one pair of left and right wheels at the angular positions along the tangential directions to turn a vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels; a turn instructing device for generating a left or right turn instruction in response to a manipulation; and a voltage applying device for applying the motors with a driving voltage at a level corresponding to the amount of pressing force to an acceleration pedal during generation of the turn instruction.
In the four-wheel vehicle of the present invention, the motors are applied with a driving voltage at a level corresponding to the amount of pressing force to the acceleration pedal, which is applied while a turning instruction is being generated, such that the motors apply rotating torques to the one pair of left and right wheels to turn the vehicle body on a neighborhood of a center point of the rotating axle of the other pair of left and right wheels, causing the turning speed to increase in accordance with the amount of pressing force applied by the driver to the acceleration pedal in the counterclockwise or clockwise turning direction. Thus, the driver can turn the vehicle body without a feeling of physical disorder as compared with a normal running operation, and accordingly turn the vehicle body to a desired position with a good operability.
The four-wheel vehicle further comprises a transmission formed with a left turn shift position and a right turn shift position in addition to shift positions for transmission, wherein the turn instructing device generates the left turn instruction when a shift lever of the transmission is moved to the left turn shift position, and generates the right turn instruction when the shift lever of the transmission is moved to the right turn shift position. According to this configuration, the driver can readily perform a left turn or a right turn operation by manipulating the shift lever of the transmission.
The four-wheel vehicle further includes a braking force applying device for applying the motors with a braking force corresponding to the amount of pressing force to a brake pedal. According to this configuration, the turning speed can be decelerated in a manner similar to a normal running operation, so that the driver can readily stop turning the vehicle body to place the vehicle at a desired position.
The four-wheel applies the motors with a slight driving force when neither the acceleration pedal nor the brake pedal is not stepped on. According to this configuration, a torque such as a creep torque of an automatic transmission is applied to the one pair of left and right wheels, so that subtle driving can be accomplished by the driver stepping on the brake pedal.